Tag Archives: Geophysics

Post navigation

Sorry to have to mention this but there has long been a problem with sewage at Lacock Abbey.

Looking north. Lacock’s 2008 south park and monastic church resistivity survey in action . Meg and Tony are standing on the church site which became a Tudor garden beneath Fox Talbot’s ornate 19th century windows.These windows were built into the monastic church cloister wall. The T junction of paths in the photo can be seen as blue bands on the resistivity plot (next image). The narrower path leads through a door beneath the smaller window into the cloisters.

We thought it had been sorted out in 1995 (and there was good archaeological recording then) but the River Avon often floods in winter and at such times the system isn’t up to the job. When the Abbey was built in the 13th century…. it was a lovely setting beside the river but to be honest it’s too low lying. The people who built the village on the higher ground knew that. When Ella Countess of Salisbury came to build her nunnery, the locals may have shaken their heads…good meadow land but don’t you know it’s on a flood plain!

Our resistivity plot is full of detail. Top is north and the blue upper edge of the image is the Abbey with other unsurveyable paths and walls as parallel bands of blue. To orientate you to the last photo, the doorway to the left of Meg leading to the cloisters is the narrow vertical blue line top centre. Below this across the broader blue path is a circular feature,once a 17th century fountain cut at its lower edge by the early 18th century garden wall, shown as a very thin blue line with the Tudor garden paths and boundary wall, now under parkland grass visible further down the plot. The old London Road is the wide feature running from right to left across the bottom of the plot. The sewage pipe route ran along the bottom edge skirting the parkland tree(which is the small blue hole in the lower left of the plot) and then curved round to the right to run along the edge of the plot . The trench was routed to avoid the detail of the Tudor garden.

One of the wonderful things about Lacock is that so much of the medieval structure survives. William Sharrington, who got the Abbey after the 1530s Dissolution, didn’t need the great monastic church so he knocked it down but he kept the cloisters and incorporated much of the dining room, dormitory, chapter house etc. in his new grand home.

The start of the pipeline on the east side of the Abbey where the old sewage works were. A medieval carved stone marking the point were the infirmary wall and drain were found.

The infirmary’s gone though. There’s just a passage from the cloisters into the east park with its name on. This was where the sick and the elderly nuns were cared for somewhere near the site of the modern sewage works.

So, in linking the Abbey sewage plant on its east side, to the village on the west, the new trench had to cross the park and follow the east and south sides of the Abbey. This was a minefield of archaeology ..and one does ones best to avoid cutting through it.. but the trench was bound to hit something.

We knew about the infirmary on the east and William Sharrington’s Tudor garden on the south. Both areas had been surveyed using geophysics and using this and all other available evidence Nathan plotted the route. Closer to the Abbey to avoid the Infirmary and swinging further south to skirt the garden.

It was bound to hit something, Lacock’s archaeologists Jane and Tony watched the work as it progressed and halted the excavation when necessary to record everything that came to light.

Lacock from the south west the trench skirting the parkland tree, the corner of the Tudor garden was just clipped by the trench before the pipeline continued round to the east skirting the 18th century bastion wall which separates Abbey and Park.

I visited before backfilling. Holes in the ground…if they can’t be avoided, are great opportunities to see and touch the story of a place and Lacock’s story is a fine one. A morning walk along the trench from the village and then to the south. Quiet along the line of the old London Road and then cutting behind a parkland tree the trench curved towards the east and clipped the very edge of the SE corner of outer Tudor garden courtyard. Nicely built, it gave reality to the ornate plan we had revealed by resisitivity in 2008. Just beyond this, the digger had clipped the lid of a deep 16th century culvert heading south from the Abbey. I turned the corner marked by the stone wall of the early 18th century garden bastion and followed the trench along the east side.

The corner of the Tudor garden exposed on the south side of the Abbey a couple of weeks ago.

There were Jane and Tony in the distance, most of the trench had exposed debris… waste picked over and discarded, that Sharrington had spread out across the park and garden during his great alteration from a religious institution to a grand country home.

Tony showed me the infirmary wall, a wide, fine ashlar stone structure. Here there was much medieval pottery, oyster shells and bones from meals that had once been eaten by the monastic community. One metal object was decorated with curving lines inlaid with silver, perhaps a pendant but Jane is looking for comparisons.

A copper alloy decorated ‘pendant’ found close to the Abbey Infirmary.

Beside the wall, there was another stone structure. To lay the pipe, the top stones had to be moved but there was enough space to send a camera down. It was a beautifully made drain… presumably nobody had glimpsed its interior for 700 years.

Photo along the the 13th century monastic drain revealed beside the infirmary. The last person to see this was probably the medieval builder.

I went on to the Lacock meeting. I was late.. looking down holes Martin they said. Take the opportunity, I encouraged them, it’s a great hole.

The day started with a cool breeze and a geophysics survey, Martin and Charlie were already on the hill, my duties were to sort out the porta-cabin and open the gate for Clive the wonderful digger driver, who did a fantastic job when we dug on Golden Cap. With the arrival of Fay and Carol we had most of the coastal team back together 🙂

Martin and Charlie in the distance

Having measured how far down the cliff the burnt material was, we knew we had to get Clive to keep going untill we found the burnt layer, at least a meter and a half deep. We started to find worked flint and even some pottery in the softer charcoal flecked layer, we had evidence of human activity, hurrah! There was even a chunk of Kimmeridge shale from about 45 miles further east along the coast. Tomorrow we will post pictures of the finds.

The turf is removed Golden Cap n the distance

We dug a test hole to see how far down we still had to go

We decided to only go down deeper in half the trench, with an option to extend if we needed to

The National Trust looks after 29 hillforts in Wessex (that’s Dorset, Somerset, Wiltshire and Gloucestershire in NT terms)

I suppose that’s not quite true NT looks after 27 and a bit, the north half of Eggardon Hill in west Dorset and the east half of Whitesheet, Stourhead Estate belong to other people. We care for only a bit of Wick Ball Camp, Dinton Park and just a rampart and ditch survives of poor old Burgh Walls near Bristol. The Edwardians built on the rest. Thank goodness Mr Wills gave NT Leigh Woods so that its neighbour Stokeleigh Camp didn’t suffer the same fate.

However, just a little west from Stokeleigh, along the Failand Ridge towards the coast at Clevedon, lies Cadbury Camp and the Trust looks after the whole of that.

The view from the west side of Cadbury looking south towards the Mendips

This is not South Cadbury on the A303 near Yeovil nor is it Cadbury Congresbury also in Somerset. It is a lesser known but no less interesting place.

It is great to visit, quiet though close to Bristol and with panoramic views across the Bristol Channel into South Wales or inland towards the Mendips.

Cadbury Camp divided into 20m grids for our geophysical survey.

I visited recently and saw the work that the Bill the ranger has organised there. The double ramparts and defensive ditches have been cleared of scrub and it looks great. There is only one gateway, on the north side overlooking Wales and that’s the place where the only excavation took place. Harold St George Grey came here in 1922 and put two trenches in and found that the ramparts are made of limestone rubble, pottery finds were Iron Age but also Roman. In fact casual finds have included other Roman evidence including sandstone roof tiles and a Roman alter fragment with the figure of the god Mars carved into it. Perhaps there was a temple or shrine up here.

It’s a place that has been visited for a long time. Flints dating to the Neolithic period have been found here and in 1856 someone found a bronze spearhead about 3000 years old. A dog walker found another one a few years ago.

Harold St George Grey’s 1922 excavation trenches across the entrance.

Back in 2001, Bristol University carried out an earthwork survey on the south side of the hillfort because they spotted a blocked entrance there. Nick and I thought we would work with them and carried out a geophysical survey of the interior. It took some time but it is good to commune with a place and get to know it. I tend to get to know a hillfort quite intimately when walking up and down taking readings with a resistivity probe.

Somebody stopped to talk and mentioned that he had lived in the nearby village of Tickenham on the south side of the ridge since he was a boy. During WWII, the soldiers from the searchlight battery used to come down the hill and drink in the pub. They were part of the defence line around Bristol to stop the bombers trashing the aircraft factory at Filton. He showed us where their huts had been. The two Marks from the university carried on surveying the blocked entrance while I did the mag and Nick did the res.

Magnetometry, see the lines of the ploughing and the two blobs where we thing the searchlights were.

When we downloaded it. The magnetometry didn’t show much just regular parallel lines, evidence of a period when the fort interior was ploughed and in addition lots of ferrous speckley bits along with two ferrous blobs. We concluded that this was where the concrete searchlight buildings had been. A subsequent meeting in Tickenham village hall gave us a clue to the speckles. Unexploded bombs which landed on Bristol were brought into the ramparts and detonated someone said.

The north-west part of the hillfort enclosure. Three parallel ditches. A Roman fortlet?

The resistivity was interesting though. Three parallel ditches formed a playing card-like corner and used the north and west ramparts of the hillfort to complete the enclosure. The Roman finds might relate to this. It’s smaller but encloses the highest part of the fort. Seems a bit like NT’s Hod Hill in Dorset. Could there have been a Roman look-out unit here?

The new information panel at the north gate showing the Iron Age round houses that people would have lived in over 2000 years ago…although we didn’t see and ring ditches on our survey.

Meet us at Tickenham village hall on October 17th and we’ll show you round.

The formal garden shown on William Woodward’s map of 1773. Traces of the pathways dividing the four lawns can be seen as parch marks and the geophysical survey but the semi-circular feature has not been detected during the surveys

We know about William Woodward’s map of 1773 showing the formal garden. This design might have included elements of the garden made for the house when it was first built in the 1660s.

From a plan of Kingston Lacy Park and Garden dated 1849, only 20 years after the obelisk was erected. The lawn is much the same today although the 17th century stable block on the right hand side of Kingston Lacy House was demolished and moved to the left in the 1880s (it’s the restaurant now).

The garden was radically changed in the 1820s and it has looked much the same ever since but there are other things here which we can’t explain.

In spring 2013, Andrew, Nigel and I walked across the South Lawn discussing the Kingston Lacy park and garden conservation plan. For many years they had noticed strange brown patterns in the grass during dry weather.

A pencil sketch of the 1773 garden over the present garden with the geophysical survey features drawn onto the plan. The house is at the top of the drawing and the obelisk at the bottom.

We decided to try to find out what they were and carry out a geophysical survey of the lawn in July as part of national archaeology festival. We plotted the parch marks, walked up and down with the resistivity and gradiometer survey machines and in 2014 Paul brought the ground probing radar from Bournemouth University and added to the ‘non-invasive’ information.

The resistivity survey plot of the South Lawn. The blue band right of centre is the path and obelisk. Kingston Lacy House lies just beyond the top edge of the survey. The red block of colour marks the position of our trench on the left side of the circular feature picked up on the survey and seen as an earthwork on the ground.

The patterns were mapped but they do not correspond with any known garden. Were they really garden features? They seem to blot out the 1773 mapped garden design and are crossed by the 1820s path to the obelisk. There seems to be a very limited time frame to fit this potential design into.

Beyond historical evidence there is only archaeology…so we dug this week’s trench, just a small one in a very large lawn, to test a place which is clear on the geophysics and visible on the ground.

One of our chunks of brick and below it the two fragments of post-medieval pottery we found, typical white ware and blue and white wares of the late 18th to early 19th century. Below them, the black blob is a late prehistoric piece of pottery over 2000 years old.

We found the lawn soil overlying a surface with lots of black clinker, the odd iron nail and bit of brick. Just a thin skim above a deeper soil but it was always moister towards the obelisk path. That’s where the water stayed during the heavy rain. That’s where the soil was deeper mixed with fragments of lime (was it reused as a garden bed? lime to make the neutral acid soil more alkaline?). The soil overlay a 250mm deep mixed clay deposit filling a curved edge cutting through the natural sand.

The slot across the natural sand and clay filling of the feature. The photo shows the edge of the pond, the soil difference between the clay filling and natural sand is clear.

The earthwork on the surface reflects this clay-lined feature which the rain water wouldn’t soak through. So our reasonable interpretation is that this was a pond and part of a garden that we have not found a documentary reference for. None of our maps show it.

So here is a story to fit the evidence. At the end of the 18th century, Kingston Lacy was re-designed by architect Robert Furze Brettingham for the then owner Henry Bankes. A new house deserves a new garden and perhaps this is shown by our geophysics and excavation..except Henry’s son William was given an obelisk from the Island of Philae in Egypt so he persuaded his father to create a garden for this extraordinary possession and the newly designed garden was swept away..

However, such formal gardens indicated by our geophysics, with a small pond like the one we found, would not be at all fashionable c.1800, a more open landscape/picturesque style might be expected so an alternative story is that the pond is earlier than the 18th century brought closer to the surface by the landscaping out of the 18th century garden in the 1820s…If we had found a good date-able piece of pottery or a white tobacco pipe bowl in the pond clay filling we would have been able to provide a more definite date for the feature.

Some of the flint from the South Lawn. The top grey chunk has been worked but then burnt in a fire. The other flakes also date to the Neolithic or Bronze Age. They probably haven’t moved far but were disturbed during 17th-19th century gardening work.

The prehistoric pot fragments and the burnt and flaked flint show that there were people living here long before Ralph Bankes first commissioned Kingston Lacy House in the 1660s, before Henry de Lacy’s medieval manor of the 13th century, before the Saxon royal farm, before the Roman town at Shapwick and even before the Iron Age hillfort of Badbury Rings.

Day 3 was probably the most changeable. The winds were the strongest, the rain the heaviest and the variations of sunlight and cloud most extraordinary.

The inclement weather gave some great brooding clouds and bright sunlight moments.

No point putting the gazebo up and the interpretation table was blown over and we decided to weight the legs and leave the pictures in a vertical position. We resorted to the scaffolding around the obelisk for shelter.

The storms across the south lawn kept blowing the table over so we weighted the legs with a shovel and mattock and Matt talked through the layers of historic gardens with the drawings in a vertical position.

The trench kept collecting water so quite hard to keep it in a photograhicable condition but things got a little better by the end of the day Matt and Rohan cleaned the surface and we could now see that the multi-coloured clay was the filling of a feature cutting through the sand. Our circular earthwork with a raised island in the middle was indeed a pond not shown on any map but clear on the geophysics.

Day 1 for me but day 2 for the boys, started a bit breezy and with blue skies and lots of clouds of all hues. Matt was finishing the section of the trench at the obelisk end, Martin was just setting up the maps and plans for everyone to see. The remaining gazebo was set up only half way, hoping it would not go the way of the other one, which flew across the lawn in the high winds and got a bent leg.

Matt working in the obelisk end section of the trench

I set to marking out the middle section next to the small sondage (a hole to find out what layers there are and how deep) and started to take off the thin layer containing clinker and brick, down to a soft layer on the path side and a very hard sandy/clay layer on the other side. There were lots of flint flakes and worked flint coming from most layers including a couple of lovely borers (like a prehistoric bradawl). Possible features were just starting to appear when the rain started, a few spits and spots, then the wind got up and large drops of rain began to increase. The call to retreat to the gazebo rang out and we made it just in time to hold the tent down as the squall hit; we had to shout to hear each other! When it stopped we went back to the trench and found we had a number of water features!

A very wet trench. the different colours of the layers showed up well after a drenching!

A quick bail out and it was back into the soggy trench.

A hand shovel makes quick work of the water. Must remember a sponge next time.

The middle section seems to have an archaeological feature in it, that may continue just into each end section. The middle section also contained a very small piece of pottery, age not certain, looks prehistoric! Matt also found a small piece of probably 18th century pottery, and some very fine glass.

The yellow hard sandy layer on the left and the softer more humic layer (feature) on the right

Martin decided to dig another sondage, to check if the hard orange/yellow surface was natural bedrock or a re-deposited layer, it looks interesting. Tomorrow will be make or break so watch this space 🙂

Matthew and I arrived this morning to find Iggy and Gordon just taking the last of the turf from the 5m by 1.4m wide trench which will be our home for the next four days. Kate arrived soon afterwards and we began to trowel..

The trench early this morning carefully stripped of turf by the Kingston Lacy garden team

A dry compacted sand with nothing in it. The trench has been positioned following resistivity, fluxgate gradiometer and ground probing radar surveys. There is a strange pattern of features across the lawn but at this location is a circular hollow about 10m across with a small mound in the middle. Possibly an ornamental pond? This and the other features are not shown on any maps of the park. They seem to hide the formal garden shown on the 1773 and 1786 maps but underlie the straight path leading to the obelisk. So is this part of a short-lived unrecorded garden c.1800…. or something else.

In front of us Kingston Lacy mansion and behind us the obelisk. It was brought to Kingston Lacy for William John Bankes and finally erected in 1829. It is covered in scaffolding at the moment while the inscriptions dating to c. 116 BC are laser scanned.

The obelisk. the eastern of a pair which once stood in front of the temple of Isis on the Island of Philae dates to the late 2nd century BC. Sent to Kingston Lacy by William John Bankes. The Duke of Wellington laid its foundation in 1827 and it was finally erected in 1829. With the Rosetta Stone it helped solve the riddle of hieroglyphics as inscribed on it are Ancient Greek and Egyptian versions of the same text. It is currently being laser scanned hence the scaffolding.

A cool strong gusty wind and our gazebo shelters rattled and shook while the information sheets to explain the shocking hole in the lawn were sent into the air and towards the house.

Bit windy our gazebo shelter were in danger of being swept away. Our maps and interpretation were regularly swept from the table and sent across the lawn

We gave up troweling and tackled the sand with mattocks. Very little in the top 100mm and then a layer sprinkled with black clinker and occasional fragments of brick.

Below the hard sandy topsoil was a similar sandy layer but with lots of black fragments of clinker in it.

We stopped and photographed it and went and had a cup of tea in the gardeners’ bothy. It was nearing the end of the day and a glimpse beneath the clinker had revealed more sand.

The black clinker layer

Is there anything there? Paul from Bournemouth Uni found us with his GPR plot. We sat round a bench and he explained that there was a buried surface reflecting back beneath the soil. Perhaps 250mm down.

We will press on tomorrow but our latest finds are micro flakes of worked flint together with chunks of burnt flint. There is a feeling that we have moved much further back in time than the 300 years we had expected but let’s see.